Dual-in-line packages (DIP's) are well known in the art. The package typically contains one or more electrical devices forming circuitry which is encapsulated in a molded body portion. The molded body has a pair of rows of parallel leads depending therefrom which are electrically connected to the circuitry. Typically, the two rows of leads are inserted into apertures in a Printed Wiring Board (PWB) and soldered to metallized patterns thereon.
One technique for fabricating such a package starts with a continuous strip of metal which is punched to form repetitive, electrically conductive patterns having a centrally located inner array of leads and an outer set of leads. Metallized ceramic substrates, having a semiconductor device thereon, are thermocompressively bonded to the inner sets of leads and the ceramic substrates are then encapsulated in an insulative material which forms the body portion of the DIP. The strip is then cut in sections which comprise the body portion with the outer leads extending laterally therefrom. The outer leads are then bent at an angle of approximately 90.degree. from the plane of the body portion for insertion into PWB's.
In order to thermocompressively bond the inner leads to the metallized ceramic substrate the leads must be relatively soft. However, in order to substantially preclude misinsertions of the outer leads into the PWB, it is necessary that they be relatively hard. Misinsertions of DIP's into PWB's in a high speed fabrication process results in costly downtime and manual replacement or repair.
Various techniques have been used to overcome the foregoing problem. In particular, the ends of the inner leads have been selectively annealed by lasers or other heating means.
Although the foregoing solutions have met with varying degrees of success, they are time consuming and costly. Accordingly, there is a need for an inexpensive and efficient technique for fabricating a lead frame having soft inner leads and hard outer leads.